The most commonly used type of molding process involves sand casting wherein a casting is formed in a sand mold, the mold being formed of a material comprising a mixture of sand grains, clay, water and additives used to improve such properties as thermal stability, surface finish, and hot strength. For convenience, this mold forming material will be referred to herein as foundry sand, or more simply sand as the greater proportion of this material is sand.
In forming a mold of this type, the foundry sand is packed around a suitable pattern, the foundry sand and pattern being surrounded by a container or flask of suitable size. The foundry sand is generally rammed in place by molding machines to produce the desired degree of packing by a squeezing action, a jolting action, a combination of squeezing and jolting or by a throwing or slinging action. The mold is then split into two halves, the cope and the drag, and the mold is ready for casting. The two halves of the mold are then closed and clamped or weighted to prevent the cope from floating when the casting is poured.
A second type of sand casting, commonly known as shell molding, involves the process of permitting sand mixed with a resin binder to come in contact with a pattern heated to an elevated temperature, approximately 350.degree. F. to 500.degree. F. Excess sand mixture is removed, leaving a thin shell of sand-plastic mixture adhering to the pattern. After heating in an oven to cure the shell, the latter is stripped from the pattern by an ejecting device. The shell halves are then clamped together and may be backed with a support assembly, for example, metal shot, prior to pouring.
While the above processes are commonly used, the processes have inherent limitations as to the fineness of surface finish, the presence of fins on the resulting casting, the presence of flasks and the limitation of speed in developing the molds. In order to alleviate these limitations, a completely automatic flaskless molding machine assembly was developed to permit the manufacture of a continuous flaskless series of molds along a pouring conveyor to form a rectilinear string of molds. Such a machine is produced and marketed under the tradename DISAMATIC and produced by DANSK INDUSTRI SYNDIKAT A/S of Copenhagen, Denmark.
Basically, the DISAMATIC machine contains a molding chamber which consists of four fixed walls and two movable walls, the first being characterized a counter pressure plate which carries the front pattern plate and the squeeze plate which forms the rear closing wall for the molding chamber. The counter pressure plate forms one-half of the mold to be mated with the other half of the mold of the preceding mold and the squeeze plate carries the rear pattern for the half of the mold to be mated with a succeeding mold. Thus, such mold formed in the molding chamber contains both halves of the mold which are integrally formed, the front half of the mold being adapted to be mated with a preceding mold and the back half being adapted to be mated with a succeeding mold. The counter pressure plate is adapted to be tilted to the horizontal position after the mold is formed and the squeeze plate is adapted to be mounted or forms the front portion of a hydraulic ram system, the hydraulic ram system being utlized to provide the hydraulic pressure to squeeze the mold and also to provide the force necessary to carry the formed mold out of the DISAMATIC machine. The DISAMATIC machine also includes a sand hopper from which sand is fed into the molding chamber positioned therebelow under controlled pressure conditions.
In operation, the molding chamber is connected to the sand hopper through an injection slot in the top of the mold chamber. The filling process is controlled by a level indicator incorporated in the sand hopper and sand is fed into the molding chamber by means of compressed air which forces the sand through the injection slot. After filling, the front tiltable pattern plate, referred to above as the counter pressure plate, is kept in a fixed position and the rear squeeze plate is moved forward under the force of the hydraulic piston to compress the sand within the molding chamber. The squeeze plate stops this movement when the pressure on the mold face has reached the desired value, which value may be adjusted. During the squeeze operation a vibratory motion may be introduced to the pattern to insure uniform density of the sand. After sufficient pressure is achieved in the mold, the front pattern plate is vibrated to strip the mold from the front pattern plate and the front pattern plate is tilted up to a horizontal position so that the molding chamber is open in the front. The rear pattern plate is then actuated by the hydraulic cylinder to push the formed mold out of the molding chamber and into engagement with the previously manufactured mold, certain of the preceding molds being supported on a table extending from within the mold chamber to a position exterior to the mold chamber. The rear pattern plate is vibrated after it has concluded its movement to the front position to strip the rear pattern plate from the formed mold. The piston is then returned to its starting position and the mold chamber is again closed to repeat the process of manufacturing a succeeding mold.
From the foregoing, it is seen that a mold is pushed into mating engagement with a previously manufactured mold to form a mold cavity therebetween, the molds being adapted to exactly mate and eliminate the fin line. As each succeeding mold is manufactured and pushed into engagement with the previously manufactured mold, the entire string is pushed forward on to a conveyor assembly, the conveyor assembly being operated by suitable rotary power devices. The molds are then conveyed to a pouring station wherein molten metal is poured into the mold cavity.
As may become apparent from the foregoing description, certain pressures are generated along the longitudinal direction of the series of mating molds, which pressures increase as the number of molds increases and, under certain conditions, may be greater than the unsupported molds may be able to withstand. Under these conditions, the molds may be crushed by the conveying force of the hydraulic ram. This undesirable crushing action of the molds is presented by sliding the manufactured molds a short distane across a supporting table by means of hydraulic ram, the molds then being positioned on a conveyor belt for movement toward a pouring and ultimate shakeout station. In conveying the molds to the pouring station, it is imperative that a certain degree of pressure be created and maintained across the face of the mold halves to insure that a proper mating of the molds is achieved during the molding process. This is accomplished by controlling the drive motor for the conveyor belt in accordance with the sensed pressure across the face of the molds, thus solving the problem of crushing of the molds and achieving uniform pressure across the mating mold halves.
The filled molds are transported from the pouring station to the shakeout station by an extension of the conveyor belt which transported the empty molds from the molding machine to the pouring station. By the time the filled molds reach the shakeout station, the metal within the molds has hardened sufficiently to retain its shape and the molds are agitated with sufficient violence to cause the molds to disintegrate. The sand residue from the disintegrated molds fall through a trap onto a used sand returned conveyor while the castings are transported to a work receiving station.
In the prior art systems the used sand is passed through a rotary screen to insure that it has been broken down into individual grains suitable for reuse in the molding machine. The rotary screen also serves to aerate and thus cool the sand which is then transported to a return sand holding tank which supplies the sand mix station previously described.
Cooling of the sand is essential inasmuch as the return sand supplied to the DISAMATIC machine for the mold operation should be about 100.degree. F. or less, while the temperature of the sand residue from the disintegrated molds may be 220.degree. F. or higher, depending on such factors as ambient temperature and humidity and the amount of times the sand has been reused during the course of a day in the molding operation.
Such prior art systems require a relatively large quantity of sand to be used in the recyle loop so that the sand will have time to cool to a temperature which will permit its reuse in the molding process. This requires an extremely large return sand holding tank and an excessive amount of sand which is costly and inefficient particularly since the sand cools slowly when packed in the holding tank.
Various attempts to solve these drawbacks have been made by providing cooling stations which add cooling water to the sand. Generally, one or more probes are positioned in the sand hopper or muller to sense either temperature or moisture content. Such probes may take the form of a temperature bulb or thermocouple for sensing temperature or electrical resistance probes for sensing conductivity (moisture). Signals derived from such sensors are used to control the addition of water to the sand. Such sytems suffer from the slow response of said sensors. Also, because the sensors are buried in the sand, they do not necessarily reflect true temperature or moisture of the sand at remote areas. Typical examples of such measuring systems are illustrated and described in U.S. Pat. Nos. 2,277,953; 2,825,946; 2,886,868; 3,083,423; 3,090,091; 3,172,175; 3,250,287; 3,580,422; Reissue 25,282; 3,601,373 and 3,958,623.
One attempt to solve the drawbacks of prior art systems included provision for measuring the volume of sand carried on a conveyor and the temperature of the sand. Such an arrangement is shown in U.S. Pat. No. 3,601,373 wherein movable feeler is caused to shift in accordance with the same level to correspondingly position a movable coil of a transformer and compensate for changes in volume. Problems with this type of system may include mechanical jamming or follow up of the roller feeler, slowness in response and inaccurate readings due either to wear of the feeler element or displacement of sand by the feeler with changes in height thereof. The temperature probe, of course, is subject to the disadvantages hereinbefore set forth.
Another attempt to solve these drawbacks in the prior art were made by providing a water quenching device at the shakeout station which sprayed cooling water onto the sand. The cooling water reduced the temperature of the sand and permitted the use of smaller holding tanks. However, to prevent the application of excess water which would mend the sand, the amount of water to be sprayed on the hot sand for cooling purposes was governed by a contact temperature sensing element. While this element provided temperature data, such data was not accurately related to actual heat content of the sand due to the variable volume of sand passing over the sensor. An example of this problem is where a relatively thin layer of hot sand causes an excessive amount of water to be sprayed on the sand causing the sand to be too wet for reuse. Alternately, an exceptionally large volume of moderately hot sand passing over the temperature sensing means would create a signal that would cause an insufficient amount of water to be sprayed over the sand for cooling purposes and the recycled sand would then be too hot for proper molding. The prior art discussed herein may be studied in more detail by referring to the aforementioned U.S. Patents and in particular to U.S. Pat. No. 3,601,373 on "Moisture Controller", issued to Nelson Hartley on Aug. 24, 1971; U.S. Pat. No. 3,800,935 on "Conveyor Drive Control System" issued to Clifford S. Montgomery on Apr. 2, 1974; and U.S. Pat. No. 3,958,623 on "Cooler-Dryer For Casting and Molding Sand" issued to Pastiaan Zissers et al., on May 25, 1976.